The present invention relates to non-ionic aryl ketone based polymeric photo-acid generators (PAGs), and more specifically to fluorinated PAG polymers comprising aryl ketone protected sulfonate ester groups that undergo photochemically induced deprotection, generating a fluorinated polysulfonic acid for lithographic applications.
Extreme ultraviolet (EUV) lithography, combined with multiple patterning enhancements, is expected to succeed current 193 nm immersion lithography as the next generation printing technique. EUV radiation, with a shorter wavelength of 13.5 nm, is expected to achieve sub-20 nm features in a single exposure process. However, more advances in efficient light sources, EUV masks, and resists are needed for EUV lithography to become a manufacturing process.
During the last few years, considerable effort has gone into the development of resists for EUV applications. However, the majority of the EUV resists have been modified from the resists developed for 193 nm and 248 nm applications.
The highest performing photoresists for 193 nm and 248 nm applications are all based on a chemical amplification mechanism. Chemically amplified photoresists utilize a catalytic mechanism to generate a relatively large number of chemical events (e.g., deprotection reactions in the case of positive tone photoresists, or crosslinking reactions in the case of negative tone photoresists). Application of a relatively low dose of radiation induces formation of the catalyst, often a strong acid, which then catalyzes the chemical events. The current positive resist compositions comprise aqueous base soluble functional groups that are sufficiently protected with acid-labile groups so that the resist initially will not dissolve in an aqueous base developer. During exposure to radiation, the photo-acid generator (PAG) present in the resist composition produces a strong acid, which then catalyzes the removal of the acid-labile groups upon heating the exposed resist layer in a post-exposure bake (PEB). This process produces aqueous base soluble material in the exposed area, which then is selectively removed with a basic aqueous developer to produce the images.
One phenomenon that limits the resolution potential of the resists developed for 248 nm, 193 nm and E-beam applications is referred to as “image blur” (see, e.g., Hinsberg et al., Proc. SPIE, (2000), 3999, 148). Image blur is generally thought to result from two contributing factors: gradient-driven acid diffusion and reaction propagation, the result being a distortion in the developable image compared to the projected aerial image transferred onto the film. This becomes critical in EUV applications because of the need for small features with low line edge roughness (LER). Therefore, a need exists to control the gradient driven acid-diffusion in the resist films.
Most widely reported PAG-bound polymers for EUV applications are ionic in nature, having a sulfonate anion attached to the polymer and a counter ion that is a sulfonium (e.g., triphenylsulfonium) or iodonium (e.g., diphenyliodonium) cation (see, for example, U.S. Pat. No. 8,057,985 B2). This type of polymer has limitations due to low incorporation of PAG 5 mol %), higher polydispersity, and poor solubility in casting solvents. These limitations prevent further improvements in resolution and LER.
Aryl ketone protecting groups have been used in organic synthesis as a photo-labile protecting group for carboxylic acids and in a few polymer-bound non-fluorinated photo-acid generators (e.g., U.S. Pat. No. 4,889,791, U.S. Pat. No. 5,624,777, JPA H10-221852).
A continuing need exists for non-ionic PAGs, which produce strong fluorinated sulfonic acids that remain attached to the polymer.